The present application claims priority to Japanese Applications Nos. P2000-101355 filed Mar. 31, 2000, P2000-101356 filed Mar. 31, 2000, P2000-101357 filed Mar. 31, 2000, and P2000-101358 filed Mar. 31, 2000, which applications are incorporated herein by reference to the extent permitted by law.
This invention relates to a separator used for a cell and, more particularly, to a non-aqueous electrolyte cell employing the separator. This invention also relates to a gelated electrolyte obtained on gelating the non-aqueous electrolyte, a non-aqueous electrolyte cell employing this non-aqueous electrolyte, a non-aqueous electrolyte used for a cell, a non-aqueous electrolyte cell employing the non-aqueous electrolyte, an electrode used in a cell and to a non-aqueous electrolyte cell employing this electrode.
Heretofore, a nickel-cadmium cell and a lead cell have been in use as a secondary cell for electronic equipment. Recently, with the progress in the electronic technology, the electronic equipment is reduced in size and improved in portability. In keeping pace theewith, a demand is raised for a higher energy density of the secondary cell for electronic equipment. However, the discharge capacity is low in the nickel-cadmium cell or lead cell, such that it is not possible to raise the energy density sufficiently.
Under these circumstances, researches are being conducted briskly in the field of the so-called non-aqueous electrolyte cell. This non-aqueous electrolyte cell features a high discharge voltage and lightness in weight.
Among known non-aqueous electrolyte cells, there are a lithium cell exploiting lithium dissolution and precipitation and a lithium ion cell exploiting doping/undoping of lithium ions. In these cells, conductivity of lithium ions play a significant role in the cell performance.
Thus, for realizing a cell having a high capacity and superior load, low-temperature and cyclic characteristics, it is crucial how the ion conductivity in the cell system of the non-aqueous electrolyte cell is to be improved.
So, in e.g., a non-aqueous electrolyte of the non-aqueous electrolyte cell, it is contemplated to raise the ionic conductivity, such as by employing carbonate-based or an ether-based non-aqueous solvent, having high chemical and electrical stability and a high dielectric constant, and by employing an imide-based lithium salt, having a degree of dissociation higher than that of routine LiPF6 or LiBF4, as an electrolytic salt.
On the other hand, if lithium ions are to be migrated between the positive and negative electrodes, the lithium ions need to be transmitted through a separator, which is known to be generally lower in ionic conductivity than the electrolyte.
For reducing the resistance of the separator to ionic conduction, it may be contemplated to increase the porosity or to reduce the film thickness.
However, in a separator in which ionic conductivity is improved by these methods, there are raised problems as to functions as the diaphragms of the positive and negative electrodes, mechanical or thermal strength or uniformity in the film thickness. Thus, these methods may not be said to be optimum.
On the other hand, if a gelated electrolyte is prepared by the combination of the routine solvent and the electrolytic salt, ionic conductivity cannot be optimum.
Moreover, if the non-aqueous electrolyte cell is produced by the combination of the routine solvent and the electrolytic salt, ionic conductivity is not sufficient. Thus, it is not that easy to provide a non-aqueous electrolyte cell which is superior in capacity, cyclic service life, heavy load characteristics and in low-temperature characteristics.
Also, if the non-aqueous electrolyte cell having a high energy density is to be realized, it is necessary to increase the capacity of the active material in the electrodes as well as to increase the amount of the non-aqueous electrolyte enclosed in the cell. In general, the non-aqueous electrolyte cell is made up of the separator and the current collector in addition to the active material. Since these components are not pertinent to charging/discharging, the volume of these components in the non-aqueous electrolyte cell is desirably as small as possible if the non-aqueous electrolyte cell is to be of high energy density.
For decreasing the volume of the separator and the current collector, the thickness of the active material may be reduced to as small a value as possible, with the electrode area being then as small as possible. However, in a well-known manner, the thick thickness of the active material leads to lowered load characteristics. If a method for producing the non-aqueous electrolyte cell or the electrode is to be optimum, it cannot be advisable to increase the thickness of the active material as high load characteristics are maintained.
It is therefore an object of the present invention to provide a separator having high ion conductivity and a non-aqueous electrolyte cell superior in capacity, cyclic durability, load characteristics and in low-temperature characteristics.
It is another object of the present invention to provide a gelated electrolyte having optimum ion conductivity and a non-aqueous electrolyte cell superior in capacity, cyclic durability, load characteristics and in low-temperature characteristics.
It is a further object of the present invention to provide a non-aqueous electrolyte having optimum ion conductivity, and a non-aqueous electrolyte cell superior in capacity, cyclic durability, load characteristics and in low-temperature characteristics.
It is yet another object of the present invention to provide an electrode which, when applied to a non-aqueous electrolyte cell, has high load characteristics, and a non-aqueous electrolyte cell having high load characteristics even if the active material is formed to a thick thickness.
In one aspect, the present invention provides a separator containing an inorganic compound having a specific inductive capacity not lower than 12.
In another aspect, the present invention provides a non-aqueous electrolyte cell including a negative electrode, a positive electrode, a non-aqueous electrolyte and a separator, wherein the separator contains an inorganic compound having a specific inductive capacity not lower than 12.
The inorganic compound exhibiting dielectric properties, added to the separator, improves the degree of dissociation of the electrolytic salt (lithium salt) impregnated into separator pores or existing in the vicinity of the separator.
The result is the decreased resistance of the lithium ions of the separator against ionic conduction and improved ionic conductivity.
Since there is no necessity of enlarging the porosity of the separator or forming the separator as a thin film, the function of the separator as a diaphragm between the positive and negative electrodes, mechanical strength and thermal strength can be achieved sufficiently.
So, in the non-aqueous electrolyte cell employing the separator, lithium ion migration between the positive and negative electrodes occurs smoothly to decrease the internal impedance to realize superior load and low-temperature characteristics. Moreover, if the ionic conductivity of the lithium ions is improved, the cyclic properties of the non-aqueous electrolyte cell are improved simultaneously.
In still another aspect, the present invention provides a gelated electrolyte obtained on gelating a non-aqueous electrolyte solution obtained in turn on dissolving an Li-containing electrolyte salt in a non-aqueous solvent, wherein the gelated electrolyte contains an inorganic compound having a specific inductive capacity not lower than 12.
In still another aspect, the present invention provides a non-aqueous electrolyte cell including a negative electrode, a positive electrode and a gelated electrolyte, a gelated electrolyte containing an inorganic compound having a specific inductive capacity not lower than 12.
The inorganic compound, exhibiting dielectric properties, added to the gelated electrolyte, improves the degree of dissociation of the electrolytic salt (lithium salt) in the gelated electrolyte. The result is the significantly improved ionic conductivity in the gelated electrolyte.
So, in the non-aqueous electrolyte cell, employing this gelated electrolyte, lithium ion migration between the positive and negative electrodes occurs smoothly to decrease the internal impedance to realize superior load and low-temperature characteristics. Moreover, if the ionic conductivity of the lithium ions is improved, the cyclic properties of the non-aqueous electrolyte cell are improved simultaneously.
In still another aspect, the present invention provides a non-aqueous electrolyte containing a non-aqueous solvent, an Li-containing electrolytic salt and an inorganic compound having a specific inductive capacity not lower than 12.
In still another aspect, the present invention provides a non-aqueous electrolyte cell comprising negative electrode, a positive electrode and a gelated electrolyte, with the gelated electrolyte containing an inorganic compound having a specific inductive capacity not lower than 12.
The inorganic compound, exhibiting dielectric properties, added to the non-aqueous electrolyte, improves the degree of dissociation of the electrolytic salt (lithium salt) in the gelated electrolyte. The result is the significantly improved ionic conductivity in the gelated electrolyte.
Moreover, in the non-aqueous electrolyte cell, employing this non-aqueous electrolyte, lithium ion migration between the positive and negative electrodes occurs smoothly to decrease the internal impedance to realize superior load and low-temperature characteristics. Moreover, if the ionic conductivity of the lithium ions is improved, the cyclic properties of the non-aqueous electrolyte cell are improved simultaneously.
In still another aspect, the present invention provides an electrode for a cell in which an electrode mixture layer containing an active material is formed on a current collector, wherein the electrode mixture layer contains an inorganic compound having a specific inductive capacity not lower than 12.
In yet another aspect, the present invention provides a non-aqueous electrolyte cell including a negative electrode, a positive electrode and a gelated electrolyte, wherein a layer of an electrode mixture containing an active material is formed on a current collector of positive electrode and/or negative electrode, with the electrode mixture layer containing an inorganic compound having a specific inductive capacity not lower than 12.
If the inorganic compound, exhibiting the dielectric performance, is added to the electrode, it improves the degree of dissociation of the electrolytic salt (lithium salt) in the non-aqueous electrolyte present in the layer of the electrode mixture or in the vicinity of the electrode. Moreover, in the non-aqueous electrolyte, present in the layer of the electrode mixture or in the vicinity of the electrode, the ionic conductivity is improved significantly, so that, if the electrode mixture is formed to an increased thickness, an optimum ionic conductivity in the electrode mixture may be achieved. If this electrode is used in the non-aqueous electrolyte cell, optimum load characteristics are achieved.
In the non-aqueous electrolyte cell, employing this electrode, the conductivity of lithium ions in the electrode mixture is optimum to decrease the internal impedance to realize superior load and low-temperature characteristics. Moreover, if the ionic conductivity of the lithium ions is improved, the cyclic properties of the non-aqueous electrolyte cell are improved simultaneously.
It will be seen from above that, since the separator of the present invention contains an inorganic compound having a specific inductive capacity not less than 12, the degree of dissociation of the lithium compound as an electrolytic salt contained in the non-aqueous electrolyte present in and near pores is improved to provide for high ion conductivity.
Since there is no necessity of increasing the porosity or reducing the thickness of the separator, the function as a diaphragm of the separator is sufficiently guaranteed, while the separator may possess sufficient mechanical or thermal strength.
In the non-aqueous electrolyte cell employing the separator, lithium ion migration between the positive and negative electrodes occurs smoothly to lower the internal impedance to realize superior load and low temperature characteristics, while the high capacity and improved cyclic characteristics may be achieved simultaneously.
Moreover, since the gelated electrolyte of the present invention includes the inorganic compound having the specific inductive capacity not less than 12, the degree of dissociation of the lithium compound, as the electrolytic salt, is increased, so that the gelated electrolyte according to the present invention is superior in dielectric constant and ionic conductivity. In addition, the gelated electrolyte according to the present invention is insusceptible to crystallization at low temperature environment.
In the non-aqueous electrolyte cell employing the gelated electrolyte, lithium ion migration between the layers of the positive and negative electrode active materials occurs smoothly to decrease the internal impedance to realize superior load and low temperature characteristics, at the same time as high capacity and superior cyclic characteristics are achieved.
Since the non-aqueous electrolyte according to the present invention contains an inorganic compound having the specific inductive capacity not less than 12, the degree of dissociation of the lithium compound, as the electrolytic salt, is increased, so that the gelated electrolyte according to the present invention is superior in dielectric constant and ionic conductivity. Also, non-aqueous electrolyte according to the present invention is insusceptible to crystallization at a low temperature environment.
Moreover, in the non-aqueous electrolyte cell employing the non-aqueous electrolyte according to the present invention, lithium ion migration between the layers of the positive and negative electrode active materials occurs smoothly to decrease the internal impedance to realize superior load and low temperature characteristics, at the same time as high capacity and superior cyclic characteristics are achieved.
Since the electrode according to the present invention contains an inorganic compound having the specific inductive capacity not less than 12, the lithium compound, as the electrolytic salt, contained in the non-aqueous electrolyte existing in and around the electrode is increased in the degree of dissociation.
In addition, in the non-aqueous electrolyte cell employing the above electrode, the non-aqueous electrolyte existing in the layer of the electrode mixture or in the vicinity of the electrode is improved to realize superior ionic conductivity, so that the ionic conductivity of the entire non-aqueous electrolyte cell is optimum to decrease the internal impedance. In the non-aqueous electrolyte cell according to the present invention, load characteristics are optimum even if the active material(s) of the positive electrode and/or the negative electrode are formed to increased thickness.
Thus, the result is the superior load and low temperature characteristics, a high capacity and appreciably improved cyclic characteristics.